1. Field of the Invention
This invention relates generally to power generation and simultaneous desalinization of salinous water, and more specifically, to improving thermal efficiency by using other waste heat sources in addition the exhaust steam to heat water used in the desalination of salinous water.
2. Description of Related Art
Power generation using steam expansion is a common process. Condensate is fed to a boiler and heated. Steam is removed from the boiler and typically superheated. It then expands across a turbine, thereby doing work. The steam is then condensed and recycled to the boiler. A moderate amount of liquid is intermittently withdrawn from the boiler to prevent sludge accumulation. Treated fresh water is added to the system to compensate for material losses. Dual purpose desalination/power plants currently in use produce fresh water by using the exhaust steam as a source of heat for a distillation unit. Essentially, the power plant's condenser is replaced by the effect of distillation unit. This allows for the efficient production of fresh water.
When desalinization plants are integrated into gas turbine power plants, they are invariably incorporated as combined cycle power plants that utilize both gas and steam turbines. In combined cycle plants, electricity is produced with high-pressure steam, generated by heat exchange with gas turbine exhaust gases, to run turbines that in turn power electric generators. In a typical case, boilers produce high-pressure steam at about 540° C. (1,000° F.). As this steam expands in the turbine, its temperature and energy level is reduced. Distillation plants need steam having a temperature of about 120° C. (248° F.) or below, and this steam can be obtained by extracting lower temperature steam at the low pressure end of the turbine after much of its energy has been used to generate electricity. This low pressure steam is then run through the distillation plant's brine heater, thereby increasing the temperature of the incoming salinous water. The condensate from the extracted steam is then returned to the boiler to be reheated.
However, typical desalination plants in commercial application reduce electricity production from combined cycle power plants because they still extract relatively high-pressure steam that would otherwise be further expanded in the steam turbine. Additionally, they do not effectively utilize other waste heat sources in the distillation process. Accordingly, a need exists for a process that increases the efficiency for desalination in a combined cycle power plant.